Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $73.55   5.714%   $77.7526   $77.75   $77.75   $77.80  
  Purchase #2 $149.52   12.336%   $167.9648   $167.96   $167.95   $168.00  
  Purchase #3 $102.37   7.807%   $110.362   $110.36   $110.35   $110.40  
  Purchase #4 $209.35   12.567%   $235.659   $235.66   $235.65   $235.70  
  Purchase #5 $181.74   8.343%   $196.9026   $196.90   $196.90   $196.90  
  Purchase #6 $58.61   11.709%   $65.4726   $65.47   $65.45   $65.50  
  Purchase #7 $215.88   13.230%   $244.4409   $244.44   $244.45   $244.40  
  7 purchase totals = $991.02       $1,098.5545   $1,098.54   $1,098.50   $1,098.70